1. Field of the Invention
This invention generally relates to the field of optical devices, and more particularly to devices that combine demultiplexing with splitting, switching, or monitoring functionality.
2. Description of the Related Art
In the rapidly evolving field of Dense Wavelength Division Multiplexing (DWDM), there is an increasing need to monitor, manage and protect optical wavelength signals as they propagate throughout different network elements. This monitoring/management ensures the reliability of the final signal and of the network system as a whole. Conventionally, this monitoring/management is achieved through the use of two separate devices: a demultiplexer and a tap monitor array. At present, these two elements are taken as separate devices because their fundamental physical mechanisms are different. Traditionally, there have been a number of ways to implement these two devices.
The most widely used demultiplexing device is the arrayed waveguide grating (AWG). AWGs, in particular, are suitable for handling a large number of wavelengths (or channels). Conventional AWGs are planar devices having a plurality of substantially parallel waveguides, each differing in length from its nearest neighbors, coupling two opposing star couplers, such as shown in, e.g., U.S. Pat. No. 5,002,350 and U.S. Pat. No. 6,266,464.
A tap monitor array is conventionally provided in one of two known devices. In a first conventional device, each output of an AWG is coupled to a 1xc3x972 coupler, which pull tap signals off each of the demultiplexed output signals. In an alternative conventional device a single 1xc3x972 directional coupler pulls a tap signal from the primary signal. The primary signal is demultiplexed by a first AWG, while the tap signal is demultiplexed by an additional AWG, such as shown in U.S. Pat. No. 5,617,234. In a similar conventional device, the tap signal is demultiplexed instead by a single channel tunable filter. This tunable filter serially selects individual wavelengths from the tap signal in the time domain.
Due to the conventional requirement that the functions of a demultiplexer and a tap array be performed by two separate devices, conventional devices have the problem of inefficient use of optical power and of space. In addition, due to fabrication differences between multiple AWGs, or among a plurality of directional couplers, the relative intensities of the demultiplexed tap signals may be different than the demultiplexed primary signals.
There remains a need for an optical device that efficiently provides multiple sets of demultiplexed signals from a single multiplexed input signal.
According to one aspect of the present invention, an optical device for receiving a primary optical signal having one or more wavelengths is provided. The optical device includes an n-way optical coupler, where n is an integer xe2x89xa72, the n-way optical coupler having one input and n outputs, the n-way optical coupler directing the optical signal into at least one of the outputs of the n-way optical coupler; and an arrayed waveguide grating. The arrayed waveguide grating includes a first optical slab having an exterior face and an interior face, the exterior face having n ports, each of the n ports being coupled to an output of the n-way optical coupler, each port receiving the optical signal emerging from the corresponding output of the n-way optical coupler. The arrayed waveguide grating also includes a waveguide array structure including a plurality of waveguides, each of the waveguides having a first end coupled to the interior face of the first optical slab, each of the waveguides having a second end. The arrayed waveguide grating further includes a second optical slab having an interior face and an exterior face, the interior face being coupled to the second end of each of the plurality of waveguides of the waveguide array structure, the exterior face having a plurality of ports. In this optical device, the optical signal emerging from each of the outputs of the n-way coupler is demultiplexed to a corresponding set of demultiplexed main diffraction order signals in the second optical slab. The n ports of the first optical slab that are coupled to the n-way optical coupler are spaced in relation to one another such that for each of the outputs of the n-way coupler, the demultiplexed main diffraction order signals corresponding to an optical signal emerging from that output of the n-way coupler do not substantially overlap with the demultiplexed main diffraction order signals corresponding to an optical signal emerging from any other of the outputs of the n-way optical coupler at the exterior face of the second optical slab. The n ports of the first optical slab that are coupled to the n-way optical coupler are also spaced in relation to one another such that demultiplexed signals of one wavelength do not substantially overlap with demultiplexed signals of another wavelength at the exterior face of the second optical slab.
In another aspect of the present invention, an optical device for receiving a primary optical signal having one or more wavelengths is provided. The optical device includes an n-way optical coupler, where n is an integer xe2x89xa72, the n-way optical coupler having one input and n outputs, the n-way optical coupler directing the optical signal into at least one of the outputs of the optical coupler, one of the outputs of the n-way optical coupler being coupled to a port of the first optical slab, another of the outputs of the n-way optical coupler being coupled to a port of the second optical slab, and an arrayed waveguide grating. The arrayed waveguide grating includes a first optical slab having an exterior face and an interior face, the exterior face having a plurality of ports; a waveguide array structure including a plurality of waveguides, each of the waveguides having a first end coupled to the interior face of the first optical slab, each of the waveguides having an second end; and a second optical slab having an interior face and an exterior face, the interior face being coupled to the second end of each of the plurality of waveguides of the waveguide array structure, the exterior face having a plurality of ports. In this device, an optical signal coupled into a port of the first optical slab is demultiplexed to a set of demultiplexed main diffraction order signals in the second optical slab, and an optical signal coupled into a port of the second optical slab is demultiplexed to a set of demultiplexed main diffraction order signals in the first optical slab.
The present invention results in a number of advantages over prior art devices and methods. For example, the devices of the present invention may be used to construct compact and power efficient devices providing both demultiplexing and switching, splitting or monitoring functionality.
Other advantages and innovations of the present invention will become apparent to those skilled in the art from the detailed description which follows and the accompanying figures. Furthermore, the preceding summary and the following description are illustrative only and do not restrict the present invention as claimed.